How can I show the GLSL code generate by node?
The easiest way to insert your own data into a node shader is to use vertex or object color (max of 3 floats each = 6 floats). Other than that you can either:


Use an image as an input, using a specific UV
lookup, and then using python to set a pixels colour.
use your own GLSL shader (which means you have to do all the lighting
yourself, and real time shadows become hard),
create your own node (which involves recompiling blender itself).


I wish there were a better way than the three above, but if there are, I am unaware of them.